The present invention relates to a harmonic rejection mixer and a phase adjustment method and in particular to a harmonic rejection mixer using a feedback control and a phase adjustment method used in the harmonic rejection mixer.
CMOS (Complementary Metal Oxide Semiconductor) transistors are applied to gigahertz RF (Radio Frequency) band by recent fine gate processing technology. Thereby, wireless system LSIs in which CMOS process is used are generally-manufactured. Although a high operation frequency can be obtained by fine transistor processing technology, process variation due to the fine processing increases. How to compensate degradation of the characteristics due to the process variation generated in this way is a problem to be solved when integrating an analog high frequency circuit.
Here, a configuration of a receiver in a broadcast system or a communication system having a wide signal band will be described. The receiver in FIG. 8 includes an antenna 200, an LNA (Low Noise Amplifier) 201, a mixer 202, a signal source 203, a filter 204, a VGA (Variable Gain Amplifier) 205, and an ADC (Analog to Digital Converter) 206. As shown in FIG. 7, when receiving a desired signal fRF (Hz) from the antenna 200, harmonics such as fRF×3 and fRF×5 may come in as disturbing wave signals in the band. In this case, harmonic components (3×fLO, 5×fLO) of an LO (local) signal outputted from the signal source 203 and the disturbing wave signals are mixed and enter the desired receiving signal band. Thereby, there is a problem that the receiving characteristics are degraded.
As one of methods solving the problem, Jeffrey A. Weldon, “A 1.75-GHz Highly Integrated Narrow-Band CMOS Transmitter With Harmonic-Rejection Mixers” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 36, NO. 12, December 2001 discloses a configuration of a harmonic rejection mixer circuit that can suppress F0×n (n=3, 5). The configuration of the harmonic rejection mixer circuit disclosed in Jeffrey A. Weldon, “A 1.75-GHz Highly Integrated Narrow-Band CMOS Transmitter With Harmonic-Rejection Mixers” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 36, NO. 12, December 2001 will be described with reference to FIG. 9. The harmonic rejection mixer circuit shown in FIG. 9 includes an LO (local) signal source 801, a ¼ frequency dividing phase shifter 302, limiter amplifiers 303 to 305, mixer circuits 306 to 308, and gain adders 309 to 311. An operation of an ordinary harmonic rejection mixer circuit will be described with reference to FIGS. 10 and 11.
If the LO signal outputted from the LO signal source 301 is an ideal square wave, the square wave signal is represented by the following formula.
                              Formula          ⁢                                          ⁢          1                ⁢                                                                                                LO          =                      An            ⁢                                          ∑                                  n                  =                  1                                ∝                            ⁢                              Cos                ⁡                                  (                                      n                    ⁡                                          (                                                                                                    ω                            Lo                                                    ⁢                          t                                                +                        φ                                            )                                                        )                                                                    ⁢                                  ⁢                  An          =                                    Sin              ⁡                              (                                  n                  ⁢                                                                          ⁢                  π                                )                                                    n              ⁢                                                          ⁢                              π                /                4                                                                        (        1        )            
Relationship between the LO signal waveform and Fourier transform is represented by the following formula.
                              Formula          ⁢                                          ⁢          2                ⁢                                                                                      LO        =                              4            π                    ⁢                      (                                          Cos                ⁢                                                                  ⁢                                  ω                  Lo                                ⁢                t                            -                                                1                  3                                ⁢                Cos                ⁢                                                                  ⁢                3                ⁢                                  ω                  Lo                                ⁢                t                            +                                                1                  5                                ⁢                Cos                ⁢                                                                  ⁢                5                ⁢                                                                  ⁢                                  ω                  Lo                                ⁢                t                            -                                                1                  7                                ⁢                Cos                ⁢                                                                  ⁢                7                ⁢                                                                  ⁢                                  ω                                      Lo                    ⁢                                                                                                                ⁢                t                ⁢                                                                  ⁢                …                                      ⁢                                                  )                                              (        2        )            
When the LO signal and an RF signal are inputted in the mixer circuits 306 to 308, as shown in FIG. 10, mixed signal components multiplied by odd numbers are outputted. In the case of an ordinary receiver, harmonic signal components of three times (third-order) and five times (fifth-order) are components that degrade the receiving characteristics. Therefore, using the characteristics of trigonometric function, as shown in FIGS. 11 and 12, the third-order and the fifth-order signal components are cancelled by multiplying LO signals having phase differences of 45 degrees and 90 degrees as LO1+√(2)×LO2+LO3. LO1 is an LO signal used as a reference, LO2 is an LO signal having a phase difference of 45 degrees from LO1, and LO3 is an LO signal having a phase difference of 90 degrees from LO1.
Specifically, when, as LO signals, a 0-degree phase difference signal is defined as VLO_0, a 45-degree phase difference signal is defined as VLO_45, a 90-degree phase difference signal is defined as VLO_90, and a frequency component of each LO signal is calculated, the LO signals are represented by the following formulas.
                              Formula          ⁢                                          ⁢          3                ⁢                                                                                                                                          VLO_                ⁢                0                            =                            ⁢                              An                ⁢                                                      ∑                                          n                      =                      1                                        ∞                                    ⁢                                      Cos                    ⁡                                          (                                              n                        ⁡                                                  (                                                                                                                    ω                                Lo                                                            ⁢                              t                                                        +                                                          π                              4                                                                                )                                                                    )                                                                                                                                              =                            ⁢                                                4                  π                                [                                                      Cos                    ⁡                                          (                                                                                                    ω                            Lo                                                    ⁢                          t                                                +                                                  π                          4                                                                    )                                                        -                                                            1                      3                                        ⁢                    Cos                    ⁢                                          (                                                                                                    ω                            Lo                                                    ⁢                          t                                                +                                                                              3                            ⁢                            π                                                    4                                                                    )                                                        +                                                                                                                      ⁢                                                                    1                    5                                    ⁢                                      Cos                    ⁡                                          (                                                                        5                          ⁢                                                      ω                            Lo                                                    ⁢                          t                                                +                                                                              5                            ⁢                            π                                                    4                                                                    )                                                                      -                                                      1                    7                                    ⁢                                      Cos                    ⁡                                          (                                                                        7                          ⁢                                                      ω                            Lo                                                    ⁢                          t                                                +                                                                              7                            ⁢                            π                                                    4                                                                    )                                                        ⁢                                                                          ⁢                  …                                            ]                                                                          =                            ⁢                                                4                  π                                [                                                                            1                                              2                                                              ⁢                    Cos                    ⁢                                                                                  ⁢                                          ω                      Lo                                        ⁢                    t                                    -                                                            1                                              2                                                              ⁢                    Sin                    ⁢                                                                                  ⁢                                          ω                      Lo                                        ⁢                    t                                    +                                                            1                                              3                        ⁢                                                  2                                                                                      ⁢                    Cos                    ⁢                                                                                  ⁢                    3                    ⁢                                          ω                      Lo                                        ⁢                    t                                    +                                                                                                                      ⁢                                                                    1                                          3                      ⁢                                              2                                                                              ⁢                  Sin                  ⁢                                                                          ⁢                  3                  ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                      1                                          5                      ⁢                                              2                                                                              ⁢                  Cos                  ⁢                                                                          ⁢                  5                  ⁢                                                                          ⁢                                      ω                    Lo                                    ⁢                  t                                +                                                      1                                          5                      ⁢                                              2                                                                              ⁢                  Sin                  ⁢                                                                          ⁢                  5                  ⁢                                                                          ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                                                                      ⁢                                                                    1                                          7                      ⁢                                              2                                                                              ⁢                  Cos                  ⁢                                                                          ⁢                  7                  ⁢                                                                          ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                      1                                          7                      ⁢                                              2                                                                              ⁢                  Sin                  ⁢                                                                          ⁢                  7                  ⁢                                      ω                    Lo                                    ⁢                  t                  ⁢                                                                          ⁢                  …                                            ]                                                          (        3        )                                          Formula          ⁢                                          ⁢          4                ⁢                                                                                                                                          VLO_                ⁢                45                            =                            ⁢                              An                ⁢                                                      ∑                                          n                      =                      1                                        ∞                                    ⁢                                      Cos                    ⁡                                          (                                              n                        ⁡                                                  (                                                                                    ω                              Lo                                                        ⁢                            t                                                    )                                                                    )                                                                                                                                              =                            ⁢                                                4                  π                                ⁢                                  (                                                            Cos                      ⁢                                                                                          ⁢                                              ω                        Lo                                            ⁢                      t                                        -                                                                  1                        3                                            ⁢                      Cos                      ⁢                                                                                          ⁢                      3                      ⁢                                              ω                        Lo                                            ⁢                      t                                        +                                                                                                                                        ⁢                                                                    1                    5                                    ⁢                  Cos                  ⁢                                                                          ⁢                  5                  ⁢                                                                          ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                      1                    7                                    ⁢                  Cos                  ⁢                                                                          ⁢                  7                  ⁢                                                                          ⁢                                      ω                    Lo                                    ⁢                  t                  ⁢                                                                          ⁢                  …                                            )                                                          (        4        )                                          Formula          ⁢                                          ⁢          5                ⁢                                                                                                                                          VLO                90                            =                            ⁢                              An                ⁢                                                                  ⁢                                                      ∑                                          n                      =                      1                                        ∞                                    ⁢                                      Cos                    ⁡                                          (                                              n                        ⁡                                                  (                                                                                                                    ω                                Lo                                                            ⁢                              t                                                        -                                                          π                              4                                                                                )                                                                    )                                                                                                                                              =                            ⁢                                                4                  π                                [                                                                            1                                              2                                                              ⁢                    Cos                    ⁢                                                                                  ⁢                                          ω                      Lo                                        ⁢                    t                                    +                                                            1                                              2                                                              ⁢                    Sin                    ⁢                                                                                  ⁢                                          ω                      Lo                                        ⁢                    t                                    +                                                                                                                      ⁢                                                                    1                                          3                      ⁢                                              2                                                                              ⁢                  Cos                  ⁢                                                                          ⁢                  3                  ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                      1                                          3                      ⁢                                              2                                                                              ⁢                  Sin                  ⁢                                                                          ⁢                  3                  ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                                                                      ⁢                                                                    1                                          5                      ⁢                                              2                                                                              ⁢                  Cos                  ⁢                                                                          ⁢                  5                  ⁢                                      ω                    Lo                                    ⁢                  t                                -                                                      1                                          5                      ⁢                                                                        2                          ⁢                                                                                                                                                                                      ⁢                  Sin                  ⁢                                                                          ⁢                  5                  ⁢                                      ω                    Lo                                    ⁢                  t                  ⁢                                                                          ⁢                  …                                            ]                                                          (        5        )            
When these LO signals are substituted in the formula of LO1+√(2)×LO2+LO3, the following formula is established.
                              Formula          ⁢                                          ⁢          6                ⁢                                                                                                            VLO_            ⁢            0                    +                                    2                        ×            VLO_            ⁢            45                    +                      VLO_            ⁢            90                          =                                            4              ⁢                              2                                      π                    ⁢                      (                                          2                ⁢                Cos                ⁢                                                                  ⁢                                  ω                  Lo                                ⁢                t                            -                                                3                  7                                ⁢                Cos                ⁢                                                                  ⁢                7                ⁢                                  ω                  Lo                                ⁢                t                            +              …                        )                                              (        6        )            
Thus, the third-order and the fifth-order components are cancelled and not generated.
Also, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2008-523734 discloses a configuration of a device for removing harmonics by a similar method as that described above. Japanese Unexamined Patent Application Publication No. 2010-109918 discloses a configuration of a receiver that can suppress a disturbing wave having frequencies near frequencies multiplied by an integer (2, 3, 4, 6, 8, 9, and so on) whose prime factors are 2 and/or 3 by using a multi-stage filter.
Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-535830 discloses a configuration of a multiplier device for suppressing harmonic components by multiplying a plurality of mixing signals by an information signal modulated by a carrier and adding a weighting coefficient to each multiplied signal.